9.2.2—The variation in the oxidation number
- Syllabus
- 9701–2028–2029
- Objective
- 9.2.2
- Level
- AS
Oxidation numbers in Period 3 oxides show how oxygen is combined
Oxidation number helps assign the formal oxidation state of the Period 3 element in its oxide. Oxygen is usually −2, so the total must match the neutral compound’s charge.
Use the formula and neutrality to calculate the oxidation number, then connect it to the element’s outer-electron arrangement and the possible oxide chemistry.
In SO₃, three oxygens contribute −6, so sulfur is +6. In Na₂O, oxygen is −2 and each sodium is +1.
Oxidation number is bookkeeping, not proof that covalent molecules contain isolated ions. Do not confuse formal oxidation state with actual charge distribution.
ConceptA-Level CAIE Chemistry AS